Radioiodine-refractory differentiated thyroid cancer (RAI-R DTC) is an aggressive form of thyroid cancer. Lenvatinib is a multikinase inhibitor approved for treatment of RAI-R DTC. The impact of tumor response and tumor burden on overall survival (OS) after lenvatinib treatment in patients with RAI-R DTC was assessed.

Data from patients treated with lenvatinib (N = 261) in SELECT were retrospectively analyzed. Patients were divided into lenvatinib responder or nonresponder subgroups and into low (≤40 mm) or high (>40 mm) tumor burden subgroups based on baseline sums of diameters of target lesions using Response Evaluation Criteria in Solid Tumors, version 1.1 (cutoff values were determined by receiver-operating characteristic analyses). Associations of tumor response and tumor burden with OS were assessed.

Median OS was prolonged in lenvatinib responders versus nonresponders (52.2 vs 19.0 months; hazard ratio [HR], 0.32; 95% CI, 0.23-0.46). Patients with a lower tumor burden who received lenvatinib had prolonged OS versus those with a higher tumor burden (median OS, not reached vs 29.1 months, respectively; HR, 0.42; 95% CI, 0.28-0.63). Baseline tumor burden was associated with OS by multivariate analysis (HR, 0.56; 95% CI, 0.35-0.89; P = .0138).

Patients with a lower tumor burden receiving lenvatinib had prolonged OS compared with those with a higher tumor burden receiving lenvatinib. Baseline tumor burden may be a prognostic factor for OS in patients with RAI-R DTC treated with lenvatinib.